1. Field of the Invention
The present invention relates to a semiconductor device. More particularly, the present invention relates to a metal oxide semiconductor (MOS) transistor device.
2. Description of the Related Art
Metal-oxide-semiconductor (MOS) transistor is one of the most important element in very large scale integrated (VLSI) circuits. The applications of MOS transistors are far and wide. In fact, microprocessors, semiconductor memory devices, power devices and so on can use MOS transistors as the basic elements. In general, a MOS transistor can be categorized as a P-type MOS transistor and an N-type MOS transistor. P-type MOS transistors have source/drain regions doped with trivalent impurities such as boron and N-type MOS transistors have source/drain regions doped with pentavalent impurities such as phosphorus or arsenic.
However, the dopants such as phosphorus, arsenic or boron inside the source/drain regions may diffuse into the channel region when a subsequent heat treatment process is carried out. This will lead to a device punch through that may ultimately affect overall performance of the device.